Summer reading is most often associated with racy romances and white-knuckle thrillers. But why not spend those extra hours of daylight flexing your mental muscles instead? Here are eight ebooks that will feed your brain and keep you entertained at the same time. Bonus: each of these ebooks is on sale for $3.99 or less until July 22. So stock up. Your brain will thank you.

1. Chaos by James Gleick

This blockbuster book first brought the butterfly effect to the forefront of general knowledge. True, chaos theory is pure mathematics—with some physics, engineering, and economics to boot—but Gleick breaks it down with a novelist's touch. Play professor at your next dinner party and regale your friends with mind-bending facts such as:

Fact #1: Chaos might not be the most accurate name for this brave new field—rather than referring to utter randomness, chaos theory moves past Newtonian physics and refers more to a given scientific phenomenon's unpredictability.

Fact #2: The famous red spot on Jupiter is a perfect example of chaos theory. After the Voyager 1 spacecraft took detailed photographs of the spot in 1979, scientists were able to actually observe a hurricane-system of swirling gas. They found that the spot is a self-organizing system that owes its existence to unpredictable phenomena. In other words, its structure is ultimately regulated by chaos.

2. Moon Shot by Jay Barbree

The gripping story of America’s space exploration from the time of Alan Shepard’s first flight until he and 11 others had walked on the moon. It's not rocket science per se, but you will still learn enough about the history of the space program to be way ahead of the curve when that much talked about Mad Men in Space show hits the airwaves. Among the impressive facts you'll pick up:

Fact #1: In addition being the second person to walk on the moon, Buzz Aldrin was the first person to take communion (or should we say "comoonion"?) on the moon. Yep, you read that correctly; Aldrin wished to mark the occasion and give thanks by taking a thimble-full of wine and wafer prepared by his pastor.

Fact #2: Another amusing fact about Aldrin: his mother's maiden name was Moon.

3. Annapurna by Maurice Herzog

An engrossing first-hand account of the first expedition in history to summit and return from Annapurna I, a peak over 8,000 meters high. Originally written in author Michel Herzog's native French, Annapurna remains just as gripping today as it was on its first publication over 50 years ago.

Fact #1: "Annapurna" is Sanskrit for "full of food." More colloquially, the name refers to the goddess of the harvest, or the "universal goddess."

Fact #2: In May of this year, The Economist reported that Annapurna is the world's deadliest summit, with a mortality rate for climbers of over 34 percent since 1950. In comparison, the statistic is just 4 percent for those who attempt to climb Everest.

4. West with the Night by Beryl Markham

One of the greatest adventure books of all time, this engrossing memoir is less about challenging your intellect and more about feeding your soul. Deftly written and heartfelt, this mediation on a life well lived will inspire your own fearless spirit.

Fact #1: Markham was the first woman to fly solo across the Atlantic from east to west.

Fact #2: Another European ex-pat living in Africa, Karen Blixen (otherwise known by her pen name Isak Dinesan) befriended Markham while they were both living in the countryside outside of Nairobi. In the film adaptation of Blixen's memoir, Out of Africa, actress Suzanna Hamilton portrays a character based on Markham.

5. Summer of '49 by David Halberstam

Halberstam’s classic #1 bestseller transports us to one magical summer when baseball’s fiercest rivalry captured the nation’s imagination and changed the sport forever. America's pastime is also a font of fascinating trivia. Impress your friends with facts from one of baseball's most memorable seasons ever:

Fact #1: The '49 baseball season took sibling rivalry to a whole different level as Joltin' Joe DiMaggio of the Yankees and Dom "Little Professor" DiMaggio of the Red Sox were pitted against each other. The latter went on to sustain a 34-game hitting streak in July and August.

Fact #2:Summer of '49 has been regarded as an allegory for a simpler time. A contemporary sports broadcaster even went so far as to claim that it was "the last moment of innocence in American life." Paul Simon, the son of a devoted Yankees fan, recalls this loss of innocence in his famous song "Mrs. Robinson," in which he laments the famous center fielder's absence in American sports culture.

6. Roosevelt: The Lion and the Fox by James MacGregor Burns

Pulitzer-Prize winner James MacGregor Burns' engrossing biography of FDR covers the beloved president's life from his year of birth to 1940. Dense with detail but wildly absorbing as a narrative, Burns provides a circumspect and detailed account of the great president's life and career, including details such as:

Fact #1: Despite the demands of navigating the country through an economic depression and a world war, Roosevelt made time for his favorite hobby: stamp collecting. At the end of his life, he had amassed over one million in his collection.

Fact #2: Though he enjoyed the longest term in office held by any president, Roosevelt made an unsuccessful bid for the Vice Presidency in 1920; he was defeated by Warren G. Harding and his running mate Calvin Coolidge.

7. Muhammad Ali by Thomas Hauser

Float like a butterfly, sting like a bee. Is there any other boxer who has attained as mythic a status as Muhammad Ali? Featuring interviews with friends, family, rivals, this definitive biography contains everything you need to know about the boxing legend, including these little known facts:

Fact #1: Ali did not box from age 25 to 28, prime years for an athlete. A fierce opponent of the Vietnam War, in 1967 he was banned and his license was suspended in response to his refusal to join the military. It was restored in 1970.

Fact #2: Before he was known as "The Greatest," Ali was known as the Louisville Lip, a nickname which references his hometown.

8. Paris Revealed by Stephen Clarke

Ah Paris! Few burgs have inspired as much reverie as this famed capital. British ex-pat Stephen Clarke shares his savoir-faire in this irreverent outsider-turned-insider guide, packed with tips and surprising facts such as:

Fact #1: Americans might not be the only ones who regard Parisians as unduly snooty—survey says that their compatriots agree. A 2010 poll by a French national news magazine found that most French people from the outer provinces regard Parisians as "arrogant, aggressive, stressed, snobbish and self-obsessed..."

Fact #2: Rumor has it that crickets abound in the Paris metro. Many travelers have reported hearing the insects chirruping, and there is even a league devoted to protecting these critters. Founded in 1992, the Protection League for the Crickets of Paris Metro are campaigning to convert an unused metro station to an auditorium of sorts where the subterranean crickets would be able to sing and breed in peace.